Clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated (Cas) were originally discovered to act as immunity defense mechanisms against foreign pathogens in prokaryotic cells (Mojica et al. (2005) J. of Molecular Evolution 60:174-182). Cas9, a protein for the type II CRISPR/Cas system, was found to exhibit DNA cleavage activity. The nuclease activity of Cas9 can be guided by a CRISPR RNA and a trans-activating CRISPR RNA complementary to a targeted sequence of DNA in the genome (Jinek et al. (2012) Science 337:816-821). Since trans-activating CRISPR RNA and CRISPR RNA can be made into a chimeric RNA containing the full function of both RNA species, artificial fusion RNA sequences, also called guide RNAs (gRNAs), were generated to target the activity of Cas9 to a target DNA sequence (Esvelt et al. (2014) eLife:e03401). A D10A mutation present in the catalytic domain of Cas9 converts it to a nickase that produces single nucleotide breaks at the target DNA (Jinek et al. (2012) Science 337:816-821). Double nicking of target DNA can increase genome editing specificity by 50-1500 fold (Ran et al. (2013) Cell 154:1380-1389), with the off-target rate as low as 1/10,000. Such specificity can make somatic genomic targeting a viable approach in treating human diseases.
Despite a high incidence, only a fraction of men diagnosed with prostate cancer develop metastases and even fewer die from the disease. The majority of prostate cancers remain asymptomatic and clinically indolent. The precise mechanisms for the development of progressive, clinically concerning prostate cancer remain elusive. Furthermore, the inability to predict prostate cancer's potential aggressiveness has resulted in significant overtreatment of the disease. The dichotomous nature of prostate cancer—a subset of life-threatening malignancies in the larger background of histological alterations lacking the clinical features implicit with that label—is a fundamental challenge in disease management. Treatment of prostate cancer, particularly of those metastatic prostate cancers remains problematic. Therefore, there is a need in the art for methods of treating a subject that may develop progressive prostate cancer.